Hi!

I find the opposite because I can place the antenna higher.
The PCI cards have the antenna behind the system unit.

I wasn't going to bring that up, but since you mention it... :-)

I find that almost all of the current wireless cards/USB adapters on
the market are far too flaky and temperamental. They also don't
provide an always-on connection in many cases--if a user logs out of
the system, the connection goes down.

And the antenna behind the case can cause a problem if the signal is
not fairly strong. That was the final problem for me.

A very effective fix that I found was to buy a router that either
offered client bridge mode (this connects a wired computer to a
wireless network) or was flashable to DD-WRT firmware (which supports
client-bridge mode). Plug such a router into the Ethernet port of the
computer in question, configure it appropriately (give it the settings
for your wireless network and a free IP address) and there you go--
freedom to locate the antenna anywhere you like and a connection that
is always on. The only possible drawback is the fact that a router
will need a power outlet of its own.

William